There is provided a conventional solar cell of a wire current collecting system comprising a solar battery module in which a photosensitive semiconductor film is formed on the cell and a large number of current collecting wires are arranged in parallel with each other and stuck on the cell.
The solar battery module is formed out of an appropriate number of solar cells, which are connected to each other, described above.
In manufacturing the solar cell, it is necessary that a large number of current collecting wires are stuck in parallel to each other on a metallic base board on which a photosensitive semiconductor film is formed. Therefore, a method is adopted in which a plurality of bobbins around which individual wires are independently wound are arranged in bobbin cassettes and wires are drawn out from these large number of bobbins and extended on a metallic base board of a work in a wiring apparatus. FIG. 12 shows a solar cell 1 made by such a method. In this solar cell 1, the adhesive double coated tape 3 is stuck at both ends of the substrate 2 of prescribed standard size. On the substrate 2, 42 pieces of fine wires 4 made of copper and coated with a conductive film, for example, the diameters of which are 0.15 mm, are laid at an interval of 5 mm. After the wires are laid, plus copper tab 5 is deposited.
As a method of drawing out such a wire 4 of a small diameter, a method is adopted in which a flange of a bobbin is set on the lower side and fixed and the wire is drawn out while the wire 4 is being unfastened. However, since a conductive film is coated on a surface of the wire 4, it is difficult to draw out the wire 4 by the above method. Accordingly, a method is adopted in which each bobbin is fixed at each bobbin holder and while the bobbin is being rotated, the wire is drawn out.
Referring to FIG. 13, an example of the manufacturing apparatus 10 used for manufacturing the above solar cell 1 will be briefly explained here.
Manufacturing apparatus 10 (wiring apparatus 10) substantially includes: a bobbin cassette 11; and a wiring machine 12. Wiring machine 12 includes: a cutter unit 13 used for returning a wire; a gripper unit 24 used for returning a wire; a unit 14 for removing looseness of the wire; a level difference roller unit 15; a gripper unit 16; a cutter unit 17; and a unit 18 used for holding the front and rear ends of the cutter.
In the bobbin cassette 11, a plurality of wire bobbin holders 20 (in this case, 21 wire bobbin holders) are respectively arranged on both sides of the frame 19. Wire bobbins B are respectively set in these wire bobbin holders 20. The wire W is drawn out from the lower side of each wire bobbin B and guided by the wire guide 21. In the wire guide 22 on the top side, 7 the wires are guided in parallel. Finally, in the cassette portion wire holding gripper 23, 42 of wires W are guided in parallel at a pitch of 5 mm and manually held.
The above wiring apparatus 10 is used as follows. For example, according to the official gazette of JP-A-9-27626, the following 6 steps are provided. The first step in which wires are drawn out from the bobbins in parallel, around which wires of prescribed number are respectively independently wound, and held by the gripper in a lump; the second step in which the wires held in a lump are drawn out from the first end portion of the work to the second end portion; the third step in which the forward end portions of the wires are pressed against the second end portion of the work so that the forward end portions of the wires are stuck; the fourth step in which holding of the forward end portions of the wires is released so that the gripper is retracted; the fifth step in which the rear end portions of the wires are pressed against the first end portion of the work so that the rear end portions of the wires are stuck; and the sixth step in which the rear end portions of the wires are cut off in a lump on the worker's side of the first end portion.
A specific means for carrying out a method, in which each bobbin is fixed at each bobbin holder and each wire is drawn out while the bobbin is being rotated, is shown by the bobbin holder 20 provided in the bobbin cassette 11 of the wiring apparatus 10 in FIG. 14.
In this case, the bobbin holder 20 includes a bobbin holder shaft 26 pivotally held by the holder 24, which is fixed at the frame 19 in the bobbin cassette 11, through the supporting bearing 25. At this bobbin holder shaft 26, the wire bobbin B is fixed by the bobbin lock nut 27 through the pushing ring Pr.
On the supporting bearing 25 of the bobbin holder shaft 26, the bearing nut 28 is mounted in such a manner that the bearing nut 28 comes into contact with the supporting bearing 25. When the bearing nut 28 is tightened to the bobbin holder shaft 26 by the tightening screw Q so that pre-load can be given, at the time of drawing out the wire W from the wire bobbin B, an appropriate braking force is applied to the wire bobbin B, so that the tension applied to the wire W can be adjusted.
However, when the above method of adjusting the tension given to the wire W is adopted, the following problems may be encountered.                (1) Since the tension applied to the wire W is low, i.e., since the tension applied to the wire W is 30 to 40 g, it is difficult to adjust the braking force. Therefore, when the wire is drawn out at high speed, i.e., when the wire is drawn out by at a length of 350 mm in 1.5 seconds, the wire W is broken.        (2) When the pre-load is reduced, at the time of drawing out the wire at high speed, the wire W is excessively drawn out by the inertia of the bobbin B and the length of the wire excessively drawn out exceeds 180 mm, which cannot be absorbed by the level difference roller unit 15. Accordingly, the apparatus will stall.        (3) The winding diameter of the bobbin B, around which the wire W is wound, is changed from 35 mm to 70 mm by the wire W to be wound. Therefore, the torque necessary for drawing out the wire is changed by the winding diameter of the bobbin B round which the wire W is wound. Therefore, when it is intended that the tension applied to the wire W is kept constant, it is impossible for the braking force to cope with the change in the torque necessary for drawing out the wire. Accordingly, there are problems in which the wire W is cut or drawn out by an excessive length.        
Further, when even one of wire W to be laid is cut, operation of the entire apparatus must be stopped. In order to restore the wiring apparatus 10, the worker must bring the wire W, which has been cut, to the wire holding gripper 23 of the cassette portion and after all the wires have been held by the wire holding gripper 23 of the cassette portion, all of the wires W must be cut off and the unnecessary wires W must be removed. After that, the wires W are delivered from the cutter unit 13 used for wire restoration to the normal gripper unit 16. Such restoration work take times, and, which results in the production line being stopped and the wires are then stored in a buffer. Accordingly, the normal production is stopped and productivity is deteriorated.
The present invention has been accomplished to solve the above problems. It is an object of the invention to provide a wire bobbin holder of a bobbin cassette in a wiring apparatus in which tension applied to a wire can be adjusted when the wire is drawn out from a bobbin mounted on the bobbin holder in the bobbin cassette of the wiring apparatus around which the wire is wound.